Conventionally, this kind of free rotation control apparatus for a hoist and traction machine is well-known which is disclosed in, for example, the Japanese Patent Publication Gazette No. Sho 54-9381. The hoist and traction machine disclosed in this Gazette, as shown in FIG. 16, is so constructed that onto a driving shaft B in association with a load sheave through a reduction gear mechanism is mounted a driven member C made not-relative-rotatable, a driving member D provided at the outer periphery with a toothed portion is threadedably engaged with the driving shaft B, between the driven member C and the driving member D are interposed a braking ratchet wheel F engageable with a braking pawl E and the braking plates G so as to constitute a mechanical brake, and the driving member D is provided with a lever H for normally or reversely driving the driving member D. The lever H is operated to normally or reversely rotate the driving member D through a change-over pawl I selectively engageable with one of the teeth N, so that the mechanical brake constituted of the braking ratchet wheel F, braking plates G, driving member D and driven member C is operated to enable a chain J engaging with the load sheave A to hoist, lower or haul a load.
The hoist and traction machine constructed as the above-mentioned is provided with a free rotation control apparatus which can quickly pull out the chain J toward the load in the no load state without operating the mechanical brake so as to elongate the chain J at the load side ,or pull the same at the no load side so as to be quickly reduced in length at the load side.
The free rotation control apparatus is provided between the driven member C and the driving member D with an elastic resistance member K for applying resistance against the movement of driving member D toward the driven member C, and a free rotation operating handle-L is fixed to the driving member D, so that, when the load sheave A is rotatably driven, a small gap Q is adapted to be formed between the free rotation operating handle L fixed to the driving member D and a stopper M fixed to an axial end of the driving shaft B. In the case of being operated for free rotation, the change-over pawl I is set to the neutral position, the operating handle L is rotatably operated, and the driving member D is screwed backwardly with respect to the braking plate G, whereby the load sheave A can freely be rotated, at which time the driving member D is suppressed of movement thereof toward the driving member C, thereby enabling the load sheave A to be held in the free rotation state without operating the mechanical brake.
Such conventional free rotation control apparatus applies resistance only by the elastic resistance member K against the movement of driving member D toward the driven member, so that, when the chain J is pulled by an excessively strong pulling force and at fast speed for pulling, the driving member D overcomes the resistance of the resistance member K to move toward the driven member C so that the mechanical brake operates not to freely operate the load sheave A, thereby creating the problem in that an input range for the pulling force of chain J during the free rotation control is restricted. Accordingly, while adjusting the pulling speed of chain J, that is, a force to pull the same, the chain J should be pulled not to operate the mechanical brake, thereby creating a problem in that it needs skill to freely rotate the load sheave A.
Regarding this problem, it has been contemplated to enlarge a spring force of the elastic resistance member K, which is interposed between the driven member C and the driving member D, and operates to suppress the movement of driving member D toward the driven member C, whereby, when the spring force is enlarged, another problem is created in that the mechanical brake is poor in its braking effect. Hence, the spring force of elastic resistance member K cannot be enlarged, resulting in that the above-mentioned problems are not solved.
The applicant of the present invention, in order to solve the above-mentioned problem, has proposed a free rotation control apparatus in which a stopper is provided at the axial end of the driving shaft, between the stopper and the driving member is provided an operating handle not-relative-rotatable with respect to the driving shaft, between the operating handle and the stopper is interposed a spring for biasing the operating handle toward the driving member, the operating handle is provided with projections facing the driving member, and at the rear surface of the driving member are provided regulation unit for regulating a relative rotation range of the driving member with respect to the driving shaft and for enabling the regulation to be released by the movement of operating handle in the direction of moving away from the driving member, and free rotation control surfaces which, when the operating handle is rotated to the regulation release position, bring the projections in elastic contact with the free rotation control surfaces by the biasing force of the spring, and apply resistance against the relative rotation of driving member with respect to the driving shaft so as to hold the free rotation state (Japanese Patent Application No. Hei 3-241372).
The free rotation control apparatus applies resistance against relative rotation of the driving member with respect to the driving shaft by the elastic contact of projections with the free rotation control surfaces through the spring and can hold the free rotation control of releasing the operation of mechanical brake, whereby such construction can obtain an effect such that the input range of the pulling force of chain during the free rotation control can be expanded, the free rotation operation can be performed without skill, and, when the chain is loaded, the operating handle automatically returns to operate the mechanical brake.
However, since the free rotation by the operating handle is performed against the aforesaid spring, when the force thereof is strengthened, the operating handle becomes heavy in operation against the spring with the result that the free rotation is poor in operability, whereby the biasing force must be set in consideration of the operability of operating handle.
Accordingly, in the above-mentioned construction, the input range of chain during the free rotation control can be expanded in comparison with the conventional example shown in FIG. 16, but the biasing force of spring cannot fully be enlarged in consideration of its operability, whereby the load is restricted when the handle automatically returns from the free rotation control state to the steady state where the mechanical brake operates, so that the input range of pulling force of chain during the free rotation control, even if expandable, is limited.